Multiphase fluid analysis

1. A method of analysing multiphase fluid flow in at least one well, the method comprises:

receiving in a storage a plurality of well pressure data from at least one pressure gauge installed on the at least one well;

processing using a processor the plurality of well pressure data to obtain a time-varying slug amplitude and a time-varying slug period for slugs in the slug flow;

analyzing, using the processor, the slug amplitudes and/or the slug periods over a period of time to thereby determine a measure of well performance to thereby characterise slug flow in the multiphase fluid flow, wherein the measure comprises a slug amplitude distribution and/or a slug period distribution over the period of time and/or wherein the measure comprises a slug amplitude average and/or a slug period average,

determining average slug amplitudes and/or average slug periods over a predetermined period of time; and

correlating the determined average slug amplitudes and/or average slug periods to well operating parameters, wherein the well operating parameters comprise lift gas rate, choke settings, fluid injection rates, gas-liquid ratio, wellhead pressure, downhole pressure, water-cut, water-oil ratio, temperature at wellhead and downhole;

controlling an oil field unit to schedule the at least one well for testing via a test manifold based on the determined measure of well performance, wherein scheduling based on the determined measure reduces an amount of time required to identify poorly performing wells;

routing, via the test manifold and according to the schedule, the at least one well to a test separator for testing.

2. The method according to claim 1 , wherein the determined measure of well performance is compared with a previous measure of well performance, and if the difference between the determined measure and the previous measure fulfils a threshold criterion, perform at least one action to investigate the cause of the difference.

3. The method according to claim 2 , wherein the action comprises prioritising the well in a well test schedule, receiving additional measurements from a well system, and taking a correcting action.

4. The method according to claim 1 , wherein the method further comprises:

determining a difference between the determined slug amplitude distribution and/or slug period distribution and a previous slug amplitude distribution and/or slug period distribution; and

if the difference fulfils a threshold criterion, prioritizing the at least one well to be tested before a second well in the well test scheduling.

5. The method according to claim 1 , wherein the processing of the plurality of well pressure data comprises the steps of

identifying in the plurality of well pressure data a plurality of well pressure maxima and a plurality of well pressure minima,

deriving a pressure difference between subsequent well pressure maxima and well pressure minima to determine time-varying slug amplitudes, and/or—deriving a time lag between two subsequent well pressure maxima and/or well pressure minima to determine time-varying slug periods.

6. The method according to claim 1 , wherein the processing of the plurality of well pressure data comprises the steps of

analysing the plurality of well pressure data using a Wavelet transform to determine a representation of the well pressure data, and

deriving time-varying slug amplitude and/or time-varying slug period from the representation of the well pressure data.

7. The method according to claim 1 , wherein the method further comprises comparing the measure of well performance for the at least one well with a reference measure of well performance for the at least one well and/or wherein the determined measure of well performance is stored in a database comprising previously determined measures of well performance for the at least one well.

8. The method according to claim 1 , wherein the multiphase fluid comprises oil, gas, water and solids.

9. The method according to claim 1 , wherein the method further comprises determining a number of slugs over a predetermined period of time and wherein the measure of well performance is further dependent on the number of slugs.

10. A non-transitory computer readable medium having stored thereon at least one code section for causing a processor to perform the steps of claim 1 .

11. The method according to claim 2 , wherein the method further comprises:

comparing the determined slug amplitude distribution and/or slug period distribution with a previous slug amplitude distribution and/or slug period distribution and if the difference fulfils the threshold criterion, prioritising the at least one well in the well test scheduling; and/or

determining average slug amplitudes and/or average slug periods over a predetermined period of time and correlating the determined average slug amplitudes and/or average slug periods to well operating parameters.

12. The method according to claim 2 , wherein the processing of the plurality of well pressure data comprises the steps of

identifying in the plurality of well pressure data a plurality of well pressure maxima and a plurality of well pressure minima,

deriving a pressure difference between subsequent well pressure maxima and well pressure minima to determine time-varying slug amplitudes, and/or—deriving a time lag between two subsequent well pressure maxima and/or well pressure minima to determine time-varying slug periods.

13. The method according to claim 2 , wherein the processing of the plurality of well pressure data comprises the steps of

analysing the plurality of well pressure data using a Wavelet transform to determine a representation of the well pressure data, and

deriving time-varying slug amplitude and/or time-varying slug period from the representation of the well pressure data.

14. The method according to claim 2 , wherein the method further comprises comparing the measure of well performance for the at least one well with a reference measure of well performance for the at least one well and/or wherein the determined measure of well performance is stored in a database comprising previously determined measures of well performance for the at least one well.

15. A system for analysing a multiphase fluid flow in at least one well transporting multiphase fluids, each well having at least one pressure gauge configured to measure well pressure, the system comprises:

a processor configured to:

receive well pressure data;

process the well pressure data to obtain a time-varying slug amplitude and a time-varying slug period for slugs in the multiphase fluid flow;

analyse the time-varying slug amplitudes and/or the time-varying slug periods over a period of time to thereby determine a measure of well performance, wherein the measure comprises a slug amplitude distribution and/or a slug period distribution over the period of time and/or wherein the measure comprises a slug amplitude average and/or a slug period average;

determine average slug amplitudes and/or average slug periods over a predetermined period of time;

correlate the determined average slug amplitudes and/or average slug periods to well operating parameters, wherein the well operating parameters comprise lift gas rate, choke settings, fluid injection rates, gas-liquid ratio, wellhead pressure, downhole pressure, water-cut, water-oil ratio, temperature at wellhead and downhole;

control an oil field unit to schedule the at least one well for testing via a test manifold based on the determined measure of well performance, wherein scheduling based on the determined measure reduces an amount of time required to identify poorly performing wells; and

routing, via the test manifold and according to the schedule, the at least one well to a test separator for testing.

16. The system according to claim 15 , the system further comprising a database for receiving well pressure data from the at least one pressure gauge for the at least one well, the processor configured to receive the well pressure data from the database.

17. The system according to claim 16 , further comprising a control unit configured to compare the determined measure of well performance with a previous measure of well performance, and, if the difference between the determined measure and the previous measure fulfils a threshold criterion, to provide a control signal indicating that an action should be performed.

18. A well system comprising

one or more wells, each well having at least one pressure gauge installed to measure a well pressure;

a common production manifold configured to receive well production output from the one or more wells;

a test manifold configured to receive well production output from one of the one or more wells; and

a multiphase fluid flow analysing system according to claim 15 ; and

an oil field unit being configured to receive the control signal from the multiphase fluid flow analysing system,

wherein the oil field unit is configured to schedule a well for testing in response to a received control signal from the multiphase fluid flow analysing system.

19. An oil field monitoring system for an oil field comprising a plurality of wells, each well having at least one pressure gauge installed to measure a well pressure and being connected to a multiphase fluid flow analysing system according to claim 15 , the oil field monitoring system comprising:

an oil field unit being configured to receive the measure of well performance from the multiphase fluid flow analysing system for each of the plurality of wells; and

an interface for outputting the measures of well performance for each of the plurality of wells.